To form a metal ingot, which is metal material cast into a suitable shape for use in various applications, metal is heated past its melting point in a furnace. Typically, the molten metal is composed of two or more materials and therefore it is important that the molten metal be sufficiently mixed to produce an ingot having a uniform structure.
Molten metal may be routed out of the furnace or other structure, mixed thoroughly, and routed back into the furnace or other structure to mix the molten metal before it solidifies. In some cases, the molten metal flows out of the furnace and back into the furnace along a curvilinear or other shaped metal transfer structure. As the molten metal moves through the metal transfer structure, the molten metal is agitated and therefore mixed. In some applications, mixing occurs using magnetic fields, such as is taught by U.S. Pat. No. 8,158,055, which issued on Apr. 17, 2012 and is incorporated herein by reference.
The described curvilinear metal transfer structures can be used in any suitable application and with any desired structure. As one additional non-limiting example, a metal transfer structure can be used to connect a furnace to a separate structure to facilitate the conveyance of molten metal between the furnace and the separate structure.
One non-limiting example of a curvilinear metal transfer structure includes a refractory housed within an outer metal casing. The molten metal, as well as combustion gases, flames and other high temperature materials, contact the refractory and therefore the refractory must have a high melting point and otherwise be capable of withstanding the high temperatures of the molten metal. The refractory insulates the outer metal casing from the molten metal to help prevent the operating temperature of the outer metal casing from reaching unsafe levels. An air gap and/or insulation may be provided between the outer metal casing and the refractory.
The refractory in contact with the molten metal typically becomes extremely hot and in some cases reaches temperatures of around 750° C., and combustion gases can heat the surface of the refractory in excess of 1200° C. Transfer of heat from the refractory to the outer metal casing causes the metal casing to heat to high temperatures during operation. As temperatures at the outer casing and the refractory change, the two components expand and contract. If the components expand and/or contract at uneven rates, distortion may occur, which can cause gaps from which the molten metal may leak. Moreover, because of the curvilinear nature of the metal transfer structure, the inner wall of the refractory is shorter than the outer wall of the refractory and thus expands less than the outer wall as the refractory heats up. Similarly, the inner wall of the outer casing is shorter than the outer wall of the outer casing and thus expands less than the outer wall as the outer casing heats up. The dissimilar heating of the inner walls versus the outer walls creates a mechanical puzzle that must be solved so that, as the refractory heats and expands, the outer casing can remain dynamic and retain its structural integrity over multiple heating and cooling cycles.